"Rebels downed two Su-25 fighters over the village of Dmytrivka in the Donetsk region, a Defense Ministry spokesman, Oleksiy Dmytrashkovsky, said by phone. Another ministry spokesman, Andriy Lysenko, later told reporters in Kiev the planes were flying at an altitude of 5,200 meters (17,000 feet) when they were brought down by a "powerful" anti-aircraft missile. The pilots ejected and their whereabouts are unknown, the ministry said on Facebook."

Reuters reports that Ukraine's Security Council claimed the missiles were fired "from the territory of the Russian Federation."

The New York Times adds that Ukraine's National Security and Defense Council in Kiev said the central government was continuing its operations against separatists and that it had retaken control of two cities in the Luhansk region.

The paper adds:

"Officials said rebels had blown up a road bridge, a railroad bridge and train tracks in the city of Gorlivka, and they reported continued fierce fighting along a section of the border with Russia that remains porous. Ukrainian forces are increasingly desperate to seal that border to prevent resupplies of weapons or new fighters from entering Ukraine.

"A Ukrainian military spokesman, Andriy Lysenko, said Russia had strengthened its troop presence along the border and cross-border gunfire had increased.

"The reported downing of the two fighter jets was a serious blow to the Ukrainian military, which has limited air power."